Without a doubt, the latest generation of optical gun sights offers many advantages over traditional iron sights. Due to this, iron sights are increasingly being relegated from a primary to a backup role. This in turn has led to a virtual explosion of aftermarket AR-15 backup iron sights over the last couple of years.

Referred to as BUIS for short, these sights are becoming increasingly popular as flattop AR's replace the conventional-carry-handle models. Currently, there are a host of models and types from which to choose.

BUIS refers to any iron sight mounted onto a rifle that is fitted with an optical sight as a primary sighting system. They come in two basic configurations, fixed or flip-up. As their name implies, fixed BUIS are mounted at the proper plane for their employment. This type of BUIS is always ready for use. Flip-up backup sights, on the other hand, rotate out of the optical sight's plane when not required. This type of sight needs to be raised prior to use. It's possible to use fixed BUIS front and rear, flip-up front and rear or to combine the two systems.

One of the advantages of a non magnified optical gun sight, such as an Aimpoint Red Dot or EoTech Holographic Weapons Sight, is the ability to mount it to co-witnesses with your iron sights. Co-witness simply means your optic is mounted on the same plane as your iron sights, allowing you to aim through your optic when using your iron sights.

One of the advantages of a non magnified optical gun sight, such as an Aimpoint Red Dot or EoTech Holographic Weapons Sight, is the ability to mount it to co-witnesses with your iron sights. Co-witness simply means your optic is mounted on the same plane as your iron sights, allowing you to aim through your optic when using your iron sights.

Both types of BUIS have their advantages and disadvantages. Fixed models tend to be simpler and more robust. Plus, as they do not need to be deployed prior to use, they are quicker into action. Their primary drawbacks are they take up part of the optic's FOV, and they can snag on things. Flip-up sights fold neatly out of the way when they are not required. This removes them from the FOV of a non magnified optic and allows them to nestle beneath a magnified optic. By folding, they also reduce the chance of being caught on something. However, they do require manual deployment before use and add complexity (and possible weakness) to the design.

Currently, there are a host of BUIS designs available from a wide variety of manufacturers. Some of these sights are very simple while others are fairly complex. When choosing one for your rifle, keep in mind that they call them a "backup" iron sight for a reason. Your optic sight is intended to be your primary sighting system. The only time you should have to employ your iron sights is if your optic fails. More than likely this means your rifle suffered a drop or blow hard enough to break your scope. So, in my opinion a BUIS should be first and foremost rugged. Look for a design that's well made from strong materials that attaches securely to the rifle.

Next, understand that in a backup or emergency sight, simple is better. Elaborate windage and elevation adjustments on the rear sight are neither necessary nor desirable. Keep in mind that realistically, you are not going to be using them to engage targets 600 meters away while cranking in windage corrections. Due to this, I consider large, easy-to-turn A2-style windage knobs a liability. The chances of them being accidentally turned, and losing your zero, is significantly greater than the likelihood of you ever needing to touch the knob in the field.

Far better is an A1-style dial with a positive lock (such as found on Troy Industries' sight) or a low-profile knob (like used on an A.R.M.S. #40-L). Elevation? Remember, we're talking about emergency use on a high-velocity 5.56. Zeroed at 50 yards the rifle will shoot point of aim at 200 yards and will only require a relatively small amount of holdover at 300 yards. Due to this, I don't feel the need for a separate elevation-adjustment system. A simple dual-aperture L-shaped flip sight is sufficient for my needs.

Rugged, flip-up sights provide failsafe backup when your primary optic or red dot sight fails. Sight post flips up easily when you need it and locks securely in place under powerful spring pressure and two locking detent balls, so it can’t be accidentally bumped down until you hit the spring-loaded button on the left side of the base to retract it. Positions apertures at the same height as factory sights, simplifying integration of these sights on your rifle. Base with sturdy side clamp and heavy duty stainless steel crossbolt attaches to any military or commercial Picatinny rail. Installs with a standard flathead screwdriver—no protruding knobs or levers to catch on brush, clothing, or other equipment. Machined from 6061 T6 aluminum and Type III hardcoat anodized for durability with Teflon® additive to resist surface abrasion; available in Black and Dark Earth. Front sight clamps to gas block accessory rail or extended handguard rail and is only ½" high when folded. Available in HK and M4 styles, both with M4-type sight post that is elevation adjustable in ½ MOA increments. Protective ears on both models shield the post from damage. Distinctive “globe” shape of HK sight aids in fast target acquisition under stress. Deep grooves in sides of M4/M16 sight post ensure a firm grasp for fast deployment. HK-Style Rear Sight bolts to flattop receiver rail and is only .460" high when folded. Flip between two same-plane apertures; large .190" aperture provides a wide field of view for close-in targets, while .070" aperture is calibrated for engaging long-range targets. Sturdy, protective “ears” guard the aperture from impact. Large adjustment wheel with deep serrations lets you change the windage setting in ½ MOA increments; positive-locking detent ensures settings change only when you want them to.

The Quick Deploy Sight System features an automatic deploy system that springs the sight up with the push of a button. Both front and rear sights lock positively in the folded and deployed positions and are made from aircraft quality aluminum and hardcoated to military specifications.

The rear sight is available with either a single large peep, single small peep, or dual peep aperture. When folded the sight measures just .435 inches from the rail.

The front sight mounts on the same plane as the rear and uses standard hardware. It is available with either a hooded or standard stem. When folded the sight measures just .435 inches from the rail.

These front sights feature either a round hooded front sight guard that allows for fast and accurate sighting or a standard style front sight guard. They feature all steel construction for superior strength in demanding conditions.The flip sight is easily concealed with the push of a button. It flips up and locks in the deployed position. This sight accepts all standard AR sight posts and hardware (Included). With this setup you get the convenience of a flip front sight with the same weight as a standard AR sight tower. This sight’s two-piece design allows it to be mounted on firearms with pinned and welded muzzle accessories. It mounts easily and securely with four cap screws.

This sight adds the convenience of a flip sight along with the versatility of a bottom picatinny rail. Available with either a round hooded front sight guard for fast and accurate sighting or a standard style front sight guard. The flip sight is easily concealed with the push of a button and locks in the deployed position. This sight accepts all standard AR sight posts and hardware (included). The picatinny bottom rail is great for laser sights, flashlights, etc. This sight’s two-piece design allows it to be mounted on firearms with pinned and welded muzzle accessories. It mounts easily and securely with four cap screws. All steel construction for superior strength in demanding conditions.

The MBUS (Magpul Back-Up Sight) is the first of it's kind: a sight designed as a low-cost, color injection molded, folding back-up sight. The MBUS fits all Picatinny rail equipped weapons, but is specifically tailored to the AR15/M16 platform.

Low-profile, flattop-mounted backup sights deploy instantly at the touch of a finger to provide relief sighting in fluid tactical situations. Drawing on their extensive manufacturing experience with high-grade, reinforced molded polymer technology, Magpul’s engineering team designed the versatile Magpul Back-Up Sight (MBUS) system to be robust, reliable, lightweight, easy to use, and affordable. Streamlined contours mean there’s nothing to snag on brush, sling, or other gear when the MBUS is folded. Spring-loaded ambi release mechanism lets you hit the grooved tab on either side, and the sight deploys and locks in place. Hit the same tabs to retract when you’re done. Integral mount requires less than 1" of MIL-STD 1913 Picatinny receiver rail space and locks securely in place with the included steel crossbolt. The A2-style front post has plenty of height adjustment for accurate sight regulation on rifles and carbines with any-length barrel; use a standard, four-prong AR-15/M16 front sight adjustment tool. Windage-adjustable rear sight has two apertures: a large, .185" peep for engaging close-range targets, and a .70" peep for longer-range shooting. Although designed for AR-type rifles and carbines, the MBUS may be installed on other weapons with Picatinny receiver rails. Available in black, Dark Earth, O.D. Green, and Foliage Green, either as matched front/rear sets or separately.